Total amount of time spent syncing WAL files to disk via issue_xlog_fsync request, in milliseconds (if track_wal_io_timing is enabled, fsync is on, and wal_sync_method is either fdatasync, fsync or fsync_writethrough, otherwise zero). Waiting for a read of the relation map file. Alone the requirement of separate fsyncs and everything is pretty bothersome. The wait_event and state columns are independent. See. Waiting to access a parallel query's information about type modifiers that identify anonymous record types. Waiting for other process to be attached in shared message queue. Waiting to read data from the client while establishing a GSSAPI session. Verify whether you have unused indexes, then remove them. Waiting for a write of a newly created timeline history file. Waiting to allocate or free a replication slot. Waiting for logical rewrite mappings to reach durable storage during a checkpoint. Principal used to authenticate this connection, or NULL if GSSAPI was not used to authenticate this connection. See, One row for each sequence in the current database, showing statistics about I/O on that specific sequence. Waiting to access predicate lock information used by serializable transactions. The pg_stat_archiver view will always have a single row, containing data about the archiver process of the cluster. If the argument is NULL, all counters shown in the pg_stat_slru view for all SLRU caches are reset. Waiting to access the transaction status SLRU cache. Waiting in main loop of WAL receiver process. Alternatively, you can invoke pg_stat_clear_snapshot(), which will discard the current transaction's statistics snapshot (if any). Waiting for a write of a WAL page during bootstrapping. Re: Improve WALRead() to suck data directly from WAL buffers when possible See Table28.5 through Table28.13. Number of disk blocks read from this table, Number of disk blocks read from all indexes on this table, Number of buffer hits in all indexes on this table, Number of disk blocks read from this table's TOAST table (if any), Number of buffer hits in this table's TOAST table (if any), Number of disk blocks read from this table's TOAST table indexes (if any), Number of buffer hits in this table's TOAST table indexes (if any). Waiting for I/O on a transaction status SLRU buffer. The pg_stat_slru view will contain one row for each tracked SLRU cache, showing statistics about access to cached pages. - a BufFreeList LWLock was getting acquired to find a free buffer for a page - to change the association of buffer in buffer mapping hash table a LWLock is acquired on a hash partition to which the buffer to be associated belongs and as there were just 16 such partitions, there was huge contention when multiple clients Waiting for parallel query dynamic shared memory allocation lock. Possible types are. Waiting for the relation map file to reach durable storage. Waiting to receive bytes from a shared message queue. Table28.12.pg_stat_database_conflicts View. Waiting for I/O on a commit timestamp SLRU buffer. When the buffer manager receives a request, PostgreSQL uses the buffer_tag of the desired page. Waiting for WAL from a stream at recovery. Text of this backend's most recent query. Waiting in main loop of autovacuum launcher process. We're sorry we let you down. Waiting for a read during reorder buffer management. Returns the process ID of the server process attached to the current session. Waiting to access the sub-transaction SLRU cache. block. Definition: lwlock.h:190. It is used per the rules above. Normally these parameters are set in postgresql.conf so that they apply to all server processes, but it is possible to turn them on or off in individual sessions using the SET command. In rows about other sessions, many columns will be null. The latter will be less if any dead or not-yet-committed rows are fetched using the index, or if any heap fetches are avoided by means of an index-only scan. Only directly connected standbys are listed; no information is available about downstream standby servers. Waiting for a read while adding a line to the data directory lock file. Waiting for WAL files required for a backup to be successfully archived. Waiting for a relation data file to reach durable storage. Thanks for letting us know we're doing a good job! Waiting in main loop of logical apply process. Table28.31.pg_statio_all_sequences View, Number of disk blocks read from this sequence. finish their input/output (I/O) operations when concurrently trying to access a page. See. Waiting in main loop of logical launcher process. The track_functions parameter controls exactly which functions are tracked. Then identify which query Streaming only works with top-level transactions (subtransactions can't be streamed independently), so the counter is not incremented for subtransactions. If the standby server has entirely caught up with the sending server and there is no more WAL activity, the most recently measured lag times will continue to be displayed for a short time and then show NULL. Waiting for the group leader to clear the transaction ID at end of a parallel operation. Waiting to allocate a new transaction ID. Waiting for a write of logical rewrite mappings. Waiting for a read when creating a new WAL segment by copying an existing one. BK_1935: "IObuffer_locks,ControlLock()"IOControlLockControlLockIOSlruSharedData. replication_origin: Waiting to read or update the replication progress. Waiting for action on logical replication worker to finish. Waiting to insert WAL into a memory buffer. Waiting for a barrier event to be processed by all backends. When the number of actual disk reads is much smaller than the number of buffer hits, then the cache is satisfying most read requests without invoking a kernel call. Here is an example of how wait events can be viewed. idle in transaction: The backend is in a transaction, but is not currently executing a query. ; Ensure that filesystem journaling is turned off for data files and WAL files. Did this page help you? ru> Date: 2015-11-19 14:04:28 Message-ID: 20151119170428.490de41d lp [Download RAW message or body] Thank you for the review. pg_stat_get_backend_wait_event ( integer ) text. shared_buffers parameter. In particular, when the standby has caught up completely, pg_stat_replication shows the time taken to write, flush and replay the most recent reported WAL location rather than zero as some users might expect. Waiting for an elected Parallel Hash participant to decide on future batch growth. So the statistics will show static information as long as you continue the current transaction. For better performance, stats_temp_directory can be pointed at a RAM-based file system, decreasing physical I/O requirements. Waiting for a write during reorder buffer management. See, One row per SLRU, showing statistics of operations. See, One row per database, showing database-wide statistics about query cancels due to conflict with recovery on standby servers. The type of event for which the backend is waiting, if any; otherwise NULL. Waiting in WAL receiver to establish connection to remote server. LWTRANCHE_BUFFER_CONTENT @ LWTRANCHE_BUFFER_CONTENT. Number of transactions in this database that have been committed, Number of transactions in this database that have been rolled back, Number of disk blocks read in this database, Number of times disk blocks were found already in the buffer cache, so that a read was not necessary (this only includes hits in the PostgreSQL buffer cache, not the operating system's file system cache), Number of live rows fetched by sequential scans and index entries returned by index scans in this database, Number of live rows fetched by index scans in this database, Number of rows inserted by queries in this database, Number of rows updated by queries in this database, Number of rows deleted by queries in this database, Number of queries canceled due to conflicts with recovery in this database. Normally, WAL files are archived in order, oldest to newest, but that is not guaranteed, and does not hold under special circumstances like when promoting a standby or after crash recovery. Waiting in main loop of logical replication apply process. However, they are also used to ensure mutual exclusion for certain internal operations such as relation extension. Returns the set of currently active backend ID numbers (from 1 to the number of active backends). If state is active this field shows the currently executing query. See, One row for each tracked function, showing statistics about executions of that function. Waiting for a newly initialized WAL file to reach durable storage. Waits for lightweight locks ( LWLock ). Waiting for a replication origin to become inactive so it can be dropped. (To prevent ordinary users from hiding their activity from the administrator, only superusers are allowed to change these parameters with SET.). checksum_last_failure timestamp with time zone. wait_event will identify the specific wait point. The server process is waiting for exclusive access to a data buffer. If you've got a moment, please tell us what we did right so we can do more of it. Avoid PostgreSQL LWLock:buffer_content locks in Amazon Aurora: Tips and best practices. Waiting to read or update transaction commit timestamps. Lag times work automatically for physical replication. BK_1935: "IObuffer_locks,ControlLock()"IOControlLockControlLockIOSlruSharedData Waiting to acquire an exclusive lock to truncate off any empty pages at the end of a table vacuumed. Waiting for a replication slot control file to reach durable storage while restoring it to memory. Send time of last reply message received from standby server. Waiting to access a shared tuple store during parallel query. You can split your All temporary files are counted, regardless of why the temporary file was created, and regardless of the, Number of deadlocks detected in this database, Time spent reading data file blocks by backends in this database, in milliseconds, Time spent writing data file blocks by backends in this database, in milliseconds, Number of queries in this database that have been canceled due to dropped tablespaces, Number of queries in this database that have been canceled due to lock timeouts, Number of queries in this database that have been canceled due to old snapshots, Number of queries in this database that have been canceled due to pinned buffers, Number of queries in this database that have been canceled due to deadlocks, Number of sequential scans initiated on this table, Number of live rows fetched by sequential scans, Number of index scans initiated on this table, Number of live rows fetched by index scans, Number of rows updated (includes HOT updated rows), Number of rows HOT updated (i.e., with no separate index update required), Estimated number of rows modified since this table was last analyzed, Last time at which this table was manually vacuumed (not counting, Last time at which this table was vacuumed by the autovacuum daemon, Last time at which this table was manually analyzed, Last time at which this table was analyzed by the autovacuum daemon, Number of times this table has been manually vacuumed (not counting, Number of times this table has been vacuumed by the autovacuum daemon, Number of times this table has been manually analyzed, Number of times this table has been analyzed by the autovacuum daemon, Number of index scans initiated on this index, Number of index entries returned by scans on this index, Number of live table rows fetched by simple index scans using this index, Number of disk blocks read from this table, Number of disk blocks read from all indexes on this table, Number of buffer hits in all indexes on this table, Number of disk blocks read from this table's TOAST table (if any), Number of buffer hits in this table's TOAST table (if any), Number of disk blocks read from this table's TOAST table indexes (if any), Number of buffer hits in this table's TOAST table indexes (if any), Number of disk blocks read from this index, Number of disk blocks read from this sequence, Number of times this function has been called, Total time spent in this function and all other functions called by it, in milliseconds, Total time spent in this function itself, not including other functions called by it, in milliseconds, Process ID of the server process handling the current session, Returns a record of information about the backend with the specified PID, or one record for each active backend in the system if, Returns the timestamp of the current statistics snapshot, Reset all statistics counters for the current database to zero (requires superuser privileges by default, but EXECUTE for this function can be granted to others. Waiting for a serialized historical catalog snapshot to reach durable storage. So the statistics will show static information as long as you continue the current transaction. Waiting for I/O on a multixact_member buffer. Waiting for the group leader to update transaction status at end of a parallel operation. This is consistent with the goal of measuring synchronous commit and transaction visibility delays for recent write transactions. To use the Amazon Web Services Documentation, Javascript must be enabled. Waiting for other Parallel Hash participants to finish hashing the inner relation. Prevent sudden database connection spikes by using a connection pool. Waiting to read or update dynamic shared memory state. Waiting for a write while initializing a new WAL file. Waiting for a read during recheck of the data directory lock file. See Table28.5 through Table28.13. pg_stat_get_backend_xact_start ( integer ) timestamp with time zone. Waiting for a read during recheck of the data directory lock file. sync: This standby server is synchronous. Wait Events of Type BufferPin, Table28.8. Number of times this function has been called, Total time spent in this function and all other functions called by it, in milliseconds, Total time spent in this function itself, not including other functions called by it, in milliseconds. a page) has to be retrieved outside the shared buffer pool. Number of WAL files that have been successfully archived, Name of the WAL file most recently successfully archived, last_archived_time timestamp with time zone, Time of the most recent successful archive operation, Number of failed attempts for archiving WAL files, Name of the WAL file of the most recent failed archival operation, last_failed_time timestamp with time zone, Time of the most recent failed archival operation. Waiting for SSL while attempting connection. Table28.19.pg_stat_subscription_stats View, Number of times an error occurred while applying changes, Number of times an error occurred during the initial table synchronization. Waiting for any activity when processing replies from WAL receiver in WAL sender process. These access functions use a backend ID number, which ranges from one to the number of currently active backends. postgres 26 Heap_Insert Waiting in WAL receiver to establish connection to remote server. These times represent the commit delay that was (or would have been) introduced by each synchronous commit level, if the remote server was configured as a synchronous standby. Top-level transaction identifier of this backend, if any. Waiting for a write while initializing a new WAL file. There have been several occasions when a query is being executed dozens of times simultaneously by one or many users. Waiting to allocate or free a replication slot. Waiting to access a parallel query's information about composite types. Waiting to read or update a process' fast-path lock information. Waiting for truncate of mapping data during a logical rewrite. The pg_stat_bgwriter view will always have a single row, containing global data for the cluster. Therefore, a bitmap scan increments the pg_stat_all_indexes.idx_tup_read count(s) for the index(es) it uses, and it increments the pg_stat_all_tables.idx_tup_fetch count for the table, but it does not affect pg_stat_all_indexes.idx_tup_fetch. See, One row for each tracked function, showing statistics about executions of that function. Waiting in main loop of autovacuum launcher process. Waiting in WAL receiver to receive data from remote server. It also tracks the total number of rows in each table, and information about vacuum and analyze actions for each table. Waiting to fill a dynamic shared memory backing file with zeroes. This counter is incremented each time a transaction is spilled, and the same transaction may be spilled multiple times. See, At least one row per subscription, showing information about the subscription workers. Waiting to access the serializable transaction conflict SLRU cache. NULL if this process is a parallel group leader or does not participate in parallel query. These numbers do not act as stated above; instead they update continuously throughout the transaction. See, One row for each table in the current database, showing statistics about accesses to that specific table. Since collection of statistics adds some overhead to query execution, the system can be configured to collect or not collect information. The idx_tup_read and idx_tup_fetch counts can be different even without any use of bitmap scans, because idx_tup_read counts index entries retrieved from the index while idx_tup_fetch counts live rows fetched from the table. A transaction can also see its own statistics (not yet flushed out to the shared memory statistics) in the views pg_stat_xact_all_tables, pg_stat_xact_sys_tables, pg_stat_xact_user_tables, and pg_stat_xact_user_functions. Waiting to read or truncate multixact information. The pg_stat_all_tables view will contain one row for each table in the current database (including TOAST tables), showing statistics about accesses to that specific table. Waiting to read or update background worker state. This facility is independent of the collector process. The pg_statio_user_tables and pg_statio_sys_tables views contain the same information, but filtered to only show user and system tables respectively. Waiting for a write to a relation data file. The LWLock:BufferIO wait event precedes the IO:DataFileRead wait event. The reported lag times are not predictions of how long it will take for the standby to catch up with the sending server assuming the current rate of replay. Each buffer header also contains an LWLock, the "buffer content lock", that *does* represent the right to access the data: in the buffer.